MEID
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Mobile Equipment Identifiers (MEIDs) are globally unique numbers indentifying a physical piece of CDMA mobile station equipment. The number format is defined by the 3GPP2 standard S.R0048 but in practical terms it is an IMEI with a two-digit hexadecimal prefix.
An MEID is 56 bits long (14 hex or 18 decimal digits). It consists of three fields, including an 8-bit regional code (RR), a 24-bit manufacturer code, and a 24-bit manufacturer-assigned serial number.
The MEID replaces the Electronic Serial Number (ESN) which has been exhausted. Special Pseudo ESNs (pESNs) can be computed from an MEID for backward compatibility. A Pseudo ESN (pESN) has 0x80 as its Manufacturer Code, followed by 24 bits of the SHA-1 hash of the 56 bit MEID. As of TIA/EIA/IS-41 Revision D and TIA/EIA/IS-2000 Rev C ESN is still a required field in many messages. In these cases pESN can be used in the ESN field and the MEID specified in the new MEID field (if any).
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[edit] Administration
The separation between International Mobile Equipment Identifiers (IMEIs) used by GSM/UTMS and MEIDs is based on the number ranges. There are two administrators; the Global Decimal Administrator (GDA) for IMEIs and the Global Hexadecimal Administrator (GHA).
As of August 2006, the TIA acts as the Global Hexadecimal Administrator (GHA) to assign MEID code prefixes (0xA0 and up), and the GSM Association acts as the Global Decimal Administrator. http://www.babt.com/gsm-imei-number-allocation.asp
The middle ground between IMEIs and MEIDs is for inter-standard "worldphone" devices. These devices will have an IMEI with a prefix of 0x99. The GDA has responsibility for the allocation of these IMEIs, since they are decimal numbers.
[edit] Display Formats
There are two standard formats for MEIDs, and both can include an optional check-digit. This is defined by 3GPP2 standard X.S0008.
The hexadecimal form is specified to be 14 digits grouped together. A check-digit can be calculated using a modified Luhn algorithm and appended to the end. The check-digit is never transmitted or stored.
The decimal form is specified to be 18 digits grouped in a 5 5 4 4 pattern. A check-digit can be calculated using a modified Luhn algorithm and appended to the end. The Luhn algorithm is different to the one used for the hexadecimal form.
[edit] pESN Conflicts
Because the pESN is formed by a hash on the MEID there is the potential for hash collisions. These will have relatively severe impacts on a pure ESN-only network as the ESN is used for the calculation of the Public Long Code Mask (PLCM) used for communication with the base-station. Duplicates within the same base-station area will result in call setup and page failures.
The probability of a collision has been investigated although further analysis using the birthday paradox may produce different results.
